The present invention relates to a semiconductor device comprising an array of memory cells in each of which a composite oxide film is used as the insulation film of an information storage capacitor and a method for the manufacture of the semiconductor device and, more particularly, a semiconductor device and a method for the manufacture of the semiconductor device, the semiconductor device being applied to a semiconductor integrated circuit including FRAM or DRAM and improved in respect of the protective structurexe2x80x94and the steps of forming the structurexe2x80x94for protecting the capacitor insulator film and the wiring in a ferroelectric memory (FRAM) comprising an array of memory cells each using an ferroelectric film as the capacitor insulation film or in a dynamic random access memory (DRAM) comprising an array of dynamic memory cells each using an ferromagnetic film as the capacitor insulator film.
Recently, attention is being drawn to a non-volatile ferroelectric memory cells (FRAM cells) using, as the inter-electrode insulation films, ferroelectric films composed of a material the perofskite structure or the lamellar perofskite structure and also to FRAM including an array consisting of the cells.
A ferroelectric film possesses the characteristic that the electric polarization once generated when an electric field is applied thereto remains even after the electric field ceases to be applied, and, when an electric field having an intensity higher than a certain value is applied, the direction of the electric polarization is reversed.
By paying attention to this polarization characteristic of this dielectric that the direction of the electric polarization thereof reverses, the technique of realizing FRAM cells by the use of ferroelectric for the insulator films of the information recording capacitors of the memory cells has been developed.
These FRAM cells are constituted in such a manner that the capacitors of the DRAM cells are replaced by ferroelectric capacitors and thus based on the method (data destructive read system) according to which, through the switching MOS transistors, the charges when the direction of the polarization is reversed or non-reversed are derived through the switching MOS transistors from the ferroelectric capacitors, and this system has the characteristic that, even if the operating power supply is turned off, the storage data written in the memory cells is not lost.
The FRAM has the feature, in view of the comparison thereof with the DRAM which is a representative of the large-capacity memories, that, since the FRAM is non-volatile, no refresh operation is needed for holding the data thereof, and no power is consumed during standby. Further, in view of the comparison of the FRAM with the flash memory which is another non-volatile memory, the FRAM has the feature that the frequency of data rewriting can be larger, and the data rewriting speed is markedly higher. Moreover, in view of the comparison thereof with the SRAM which is used for memory cards etc. and can be backed up by battery, the FRAM has the feature that the power consumption thereof is smaller, and the cell area can be decreased to a substantial degree.
The FRAM which has features as mentioned above are expected much connection with the replacement thereby of the existing DRAM, flash memory and SRAM, the application thereof to logic hybrid devices, etc. Further, the FRAM can operate at high speed without the use of a battery and, therefore, the development thereof into non-contact cards such as RF-ID: Radio Frequency-Identification etc, is being started.
As mentioned above, the FRAM cell can operate at high speed and yet with a low power consumption and, thus, is expected to be integrated at a high degree of integration. Thus, the reduction in area of the memory cell and a manufacturing process accompanied by a reduced deterioration of the ferromagnetic need to be examined. Further, the multi-layer wiring technique which is indispensably necessary in case of mounting the existing FRAM device compositely with other devices and for realization of a high-degree integration thereof has not been established yet at present.
The reason why it is difficult for semiconductor integrated circuits with FRAM devices mounted thereon to be realized in a multi-layer wiring structure lies in the fact that the ferroelectric material is very weak to a reducing atmosphere (particularly, a hydrogen atmosphere). Most of the existing LSI processes are of the type in which hydrogen is mixed in, which gives a serious problem to the manufacture of FRAM.
That is, according to the conventional technique of forming FRAM cells, as shown in, e.g. FIG. 1, after an element isolation region 102 is formed in a silicon substrate 101, a gate insulation film 103 is formed, a gate electrode 104, a gate protecting insulation film 105, and drain-source regions (diffused layer regions) 106 and 107 are successively formed, whereby a pass transistor (switching MOS transistor) is formed. Thereafter, a BPSG film 201 or the like is deposited and flattened, and, on the upper layer thereof, a lower electrode 401, a ferroelectric film 402 and an upper electrode 402 are deposited in this order and subjected to patterning, respectively, to dispose a ferroelectric capacitor, on the upper layer thereof, an insulation film (such as, e.g. plasma TEOS) 207 is deposited, through a contact hole bored in the insulation film 207 and the BPSG film 201, a local wiring 301 is provided, further, on the upper layer thereof, an insulation film 203 is deposited, and through contact holes bored in this insulation film 203 etc., metal wirings 302 and 303 are provided, after which a passivation film is provided for protection.
Here, as the ferroelectric of the FRAM cell capacitor, there are used oxides containing the perofskite structure such as PZT (Pb (Zr, Ti) O3, lead zirconate titanate), SBT (SrBi2Ta2O9: strontium bismuth tantalum), BIT (Bi4Ti3O12), etc. or such oxides which have each been partially replaced by a substitute element.
Further, generally in case PZT or SBT is used as the ferroelectric material, a rare metal or an electrically conductive oxide such as Pt (platinum), Ir, Ir oxide (IrO2), Ru, Ru oxide (RuO2), LSCO or the like. is used as the electrode material of the ferroelectric capacitor.
As described above, in case of forming the ferroelectric capacitor, generally the lower electrode is formed by the use of Pt, and thereafter, the ferroelectric thin-film is formed, in which case, when the ferroelectric thin-film is formed and crystallized, a high-temperature oxygen annealing is needed.
Here, in case PZT is used as the ferroelectric material, the capacitor characteristics are deteriorated by the occurrence of a defect due to the diffusion of Pb in the PZT in case the oxidation is insufficient. The oxygen annealing temperature necessary to effect a sufficient oxidation so as to avoid the above-mentioned deterioration is ordinarily 600xc2x0 C. to 700xc2x0 C.
Further, in case a bismuth lamellar compound such as SBT or the like is used as the ferroelectric material, the necessary oxygen annealing temperature is ordinarily so high as 800xc2x0 C.
However, in case of the structure in which the lower electrode (such as, e.g. Pt) of the ferroelectric capacitor and the transfer gate (pass transistor) are connected to each other by means of a polycrystalline silicon plug, there arises the problem that, when the oxygen annealing of a high temperature as mentioned above is performed, the lower electrode composed of Pt reacts with the polycrystalline silicon plug into a silicide or the problem that the polycrystalline silicon plug is oxidized.
On the other hand, in case of the structure in which the upper electrode of the ferroelectric capacitor and the transfer gate are connected to each other directly by a local electrode wiring comprising a buried contact, it becomes difficult to form the local electrode wiring for directly connecting the upper electrode and the pass transistor to each other in respect of the aspect ratio or the step coverage related to the miniaturization. Further, in case PZT or SBT is used as the ferroelectric material, the problem to be taken up is the reducing atmosphere at the respective CVD (chemical vapor deposition) steps carried out for the formation of electrode wirings after the formation of ferroelectric thin-film, that is, there arises the problem that the characteristics of the ferroelectric material are deteriorate by the reducing reaction.
In other words, if, in case of forming the local electrode wiring for connecting the upper electrode and the transfer gate to each other, it is attempted to effect the burying of the tungsten plug by forming a W (tungsten) film in a strong reducing atmosphere (a hydrogen-based gas) using a metal CVD apparatus as is used in connection with DRAM, then the characteristics (electric characteristics such as the amount of remanent polarization etc.) of the ferroelectric capacitor are deteriorated, so that this technical measure cannot be employed.
In contrast, if, in case of forming the local electrode wiring for connecting the upper electrode and the transfer gate to each other, it is tried to form an aluminum wiring film by the use of a MO (Metal Organic) CVD method, the deterioration in characteristics of the ferroelectric capacitor is also caused since it is not probable that there is no reducing atmosphere at all (the hydrogen group component including the source material cannot be perfectly removed).
That is, in case of the conventional Si semiconductor manufacturing method, a step for depositing an insulation film and a process needing a hydrogen atmosphere from the necessity of stabilizing the contact of the contact point between Al the contact and Si have been regarded as indispensable. However, the ferroelectric film has the weak point that it is weak to a hydrogen atmosphere and water as mentioned above. It is because, if the hydrogen gas or water reaches the ferroelectric, oxygen, then voids of oxygen are caused in the crystal structure of the ferroelectric being an oxide, and thus, the use of a step in which hydrogen or water is produced must be avoided after the formation of the capacitor. Further, the step of depositing, as the insulation film on the capacitor, plasma TEOS as mentioned above is employed reluctantly for the reason that the damage inflicted on the ferroelectric by the hydrogen produced in this step is relatively small as compared the damage caused by water.
On the other hand, in the case of DRAM, recently it, has been tried to use a high-permittivity dielectric material having the perofskite structure or the lamellar perofskite structure for the capacitor insulation film, but the high-permittivity dielectric material used in DRAM is likewise not free from the problem that its characteristics are deteriorated by a reducing reaction.
That is, the degree of integration of DRAM is enhanced year by year, but, even if the size thereof is decreased, the electric capacity of the respective dielectric capacitor which stores charges must be kept at about 30 fF or higher.
For this, the effective area of the capacitor must be increased, the thickness of the dielectric film must be decreased, or the dielectric constant of the dielectric material must be enhanced. According to the conventional technique, improvements are made in respect mainly of the first and second cases of the above-mentioned three cases, and examinations have been made for forming the capacitor into a three dimensional structure and making it thinner, but in case of the conventional SiO2 dielectric films, the improvement in three-dimensional structuring and thinning of the capacitors are reaching the limit. Thus, expectations for thin films of high-permittivity dielectric which have a relative permittivity of 50 or higher such as, e.g. thin films of BST ((Ba, Sr) TiO3) are increasing, but, in case of such thin films, it is desired to remove the after-steps in which hydrogen or water is produced, exactly as in the case of the afore-mentioned ferroelectric films.
Further, in case of forming a semiconductor device such as FRAM or DRAM using a ferroelectric material or a high-permittivity dielectric material, an annealing in an oxygen atmosphere (oxidation step) is needed, after the deposition or etching of the ferroelectric film or a high-permittivity dielectric film is performed, for the purpose of recovering from the characteristics change (the change in characteristics of the ferroelectric film or the high-permittivity dielectric film) due to the release of the stress at the time of deposition or due to the damage inflicted on at the time of etching.
So far, in fear of the fact that, as a result of the annealing in an oxygen atmosphere, the wiring and wiring electrodes which have already been formed may be oxidized to have higher resistance, rendered into abnormal shapes due to an abnormal oxidation to cause cracks, generally there has been formed a capacitor of the structure in which electrodes are provided on both surfaces of a ferroelectric film or a high-permittivity dielectric film, and, after it is annealed in an oxygen atmosphere, the wiring layer between the capacitor electrode and the diffused layer already formed on the semiconductor substrate and the wiring contact are formed.
The above-mentioned formation of the contact wiring was easy when the degree of integration was relatively low and the size of chips was relatively large, but as the degree of integration is becoming higher and higher, the vertical portion of the device becomes high in density, contact wiring layers with vary small diameters are formed, and a structure in which, on an element, another is formed in a stacked manner is required. In this case, the wiring layers must inevitably be formed before the formation of the high-permittivity element or the ferroelectric element.
However, in case the respective wiring layer was formed before the formation of the high-permittivity dielectric element or the ferroelectric element, the wiring layer was oxidized into high resistance in case the wiring layer was formed before the formation of the high-dielectric element or the ferroelectric element, and thus, a sufficiently low wiring resistance could not be obtained. Further, even if a metal wiring material which is generally regarded as strong or resistant to oxidation was used to form the wiring layer before the formation of the high-dielectric element or the ferroelectric element, an abnormal oxidation was caused notwithstanding, causing cracks. As stated above, there were various problems, so that a low wiring resistance could not be realized.
Further, the step of performing sintering at 450xc2x0 C. by the use of a gas mixture of hydrogen and nitrogen as is performed in an ordinary semiconductor device manufacturing process in order to lower the contact resistance between the active layer of MOSFET and the contact wiring layer resulted in the fact that the high-permittivity dielectric film or ferroelectric film was reduced by the hydrogen, as a result of which the characteristics of the high-permittivity dielectric element or the ferroelectric element were deteriorated, and thus, the sintering step could not be adopted. Thus, it has been very difficult to control the characteristics of the MOSFET and the contact.
It is the object of the present invention to provide a semiconductor device having a structure constituted in such a manner that the various problems mentioned above can be eliminated; and the ferroelectric film or the high-permittivity dielectric film can be protected from being damaged by hydrogen or water and also to provide a method for the manufacture of the semiconductor device.
Another object of the present invention is to provide a semiconductor device constituted in such a manner that the deterioration of the remanent polarization (QSW) of the ferroelectric film can be held down low and also to provide a method for the manufacture of the semiconductor device.
Still another object of the present invention is to provide a semiconductor device constituted in such a manner that the deterioration in characteristics of the high-permittivity dielectric film or the ferroelectric film due to a reducing atmosphere can be prevented and also to provide a method for the manufacture of the semiconductor device.
Still another object of the present invention is to provide a semiconductor device constituted in such a manner that the wiring layer and the element which have already been formed before the formation of the ferroelectric film or high-permittivity dielectric film can be protected from bering oxidized, and the good electrical conductivity and shapes of the wiring layer and the element can be maintained and supplied and also to provide a method for the manufacture of the semiconductor device.
Still another object of the present invention is to provide a semiconductor device constituted in such a manner that, in case of manufacturing the ferroelectric memory cells, the deterioration in characteristics of the ferroelectric capacitor can be prevented, and a process integration is made possible and also to provide a method for the manufacture of the semiconductor device.
Still another object of the present invention is to provide a semiconductor device constituted in such a manner that, in case of manufacturing a ferroelectric memory having a multi-layer wiring structure comprising at least two or more layers, the bit lines connected to the cells can be formed by the multi-layer wiring, and thus, the degree of integration can be enhanced, and the mounting of the semiconductor device compositely with other devices can be easily realized and also to provide a method for the manufacture of the semiconductor device.
In order to achieve the above-mentioned objects, the semiconductor device according to the present invention comprises:
a switching transistor including a drain region and a source region which are comprised of an impurity-diffused region formed in the surface layer portion of a semiconductor substrate;
a first insulation film formed above the semiconductor substrate containing the transistor;
a capacitor formed on the upper layer side of the first insulation film and comprised of a lower electrode, an inter-electrode insulation film composed of one of ferroelectric and high-permittivity dielectric, and an upper electrode;
a second insulation film which is formed, before the formation of the inter-electrode insulation film, so as to cover the side surface portion of the inter-electrode insulation film, whereby the side surface of the inter-electrode insulation film which is formed later is protected;
an electrode wiring which connects one of the drain region and the source region and one of the upper electrode and the lower electrode of the capacitor to each other; and
a wiring formed above the semiconductor substrate and connected to the other one of the drain region and the source region.
Further, the semiconductor device according to the present invention comprises:
a switching transistor including a drain region and a source region which are comprised of an impurity-diffused region formed in the surface layer portion of a semiconductor substrate;
a first insulation film formed above the semiconductor substrate containing the transistor;
a capacitor formed on the upper layer side of the first insulation film and comprised of a lower electrode, an inter-electrode insulation film composed of one of ferroelectric and high-permittivity dielectric, and an upper electrode;
one of a silicon nitride film and a titanium oxide film formed, with respect to the capacitor so as to cover the side surface of the inter-electrode insulation film which is exposed between the lower electrode and the upper electrode;
an electrode wiring which connects one of the drain region and the source region and one of the upper electrode and the lower electrode of the capacitor to each other; and
a wiring formed above the semiconductor substrate and connected to the other one of the drain region and the source region.
Further, the method for manufacturing a semiconductor device according to the present invention comprising the steps of
forming, in the upper layer portion of a semiconductor substrate, a switching transistor including a drain region and a source region which are comprised of an impurity-diffused layer;
forming a first insulation film above the semiconductor substrate containing the transistor;
forming, on the first insulation film, a first electrically conductive film for a lower electrode;
forming a second insulation film on the first electrically conductive film;
forming a dielectric-film burying opening in the second insulation film selectively;
forming a dielectric film on the second insulation film containing said dielectric-film burying opening, the dielectric film constituting an inter-electrode insulation film composed of one of ferroelectric and high-permittivity dielectric;
removing the portion, lying on the second insulation film, of the dielectric film which is other than the dielectric film portion buried in the dielectric-film burying opening, the dielectric film portion buried in the dielectric-film burying opening being for a charge storage capacitor;
forming a second electrically conductive film for the upper electrode, on the second insulation film and the dielectric film; and
forming the charge storage capacitor by successively patterning the second electrically conductive film, the second insulation film and the first electrically conductive film.
Further, the semiconductor device according to the present invention comprises:
a first diffused layer formed in a semiconductor substrate;
a first insulation film formed above the first diffused layer;
a first electrically conductive film formed above the first insulation film;
a first metal wiring buried in a first contact hole bored in the first insulation film to connect the first diffused layer and the first electrically conductive film; and
a first wiring layer protecting film formed so as to cover the upper surface of at least one of the first electrically conductive film and the first metal wiring, the first wiring layer protecting film comprising one of a nitride-based film and a titanium oxide film.
Further, the semiconductor device according to the present invention comprises:
a first diffused layer formed on a semiconductor substrate;
a first insulation film formed above the first diffused layer;
a first contact wiring layer composed of a metal wiring material buried in a first contact hole bored in the first insulation film;
a first wiring layer protecting film formed so as to cover at least a part of the upper surface of the first contact wiring layer;
a first electrode wiring layer formed above the first insulation film;
a second insulation film formed, on the first electrode wiring layer, one of a high-permittivity dielectric film and a ferroelectric film;
a second electrode wiring layer formed on the second insulation film;
a third insulation film formed on the second electrode wiring layer; and
a second contact wiring layer buried in a second contact hole bored above the first contact wiring layer of the third insulation film to connect the second electrode wiring layer and the first contact wiring layer.
Further, the semiconductor device according to the present invention comprises
a first diffused layer formed on a semiconductor substrate;
a first insulation film formed above the first diffused layer;
a first electrically conductive film formed on the first insulation film;
a first metal wiring layer buried in a part of a plurality of first contact holes bored in the first insulation film and connecting the first diffused layer and the first electrically conductive film;
a first contact wiring layer comprised of the metal wiring material buried in another part of the plurality of first contact holes;
a first wiring layer protecting film formed so as to cover at least a part of the upper surface of the first electrically conductive film, the upper surface of the first metal wiring layer and the upper surface of the first contact wiring layer;
a second insulation film formed on the first wiring layer protecting film and the first insulation film;
a first electrode wiring layer formed above the second insulation film;
a third insulation film formed, on the first electrode wiring layer, of one of a high-permittivity dielectric film and a ferroelectric film;
a second electrode wiring layer formed on the third insulation film;
a fourth insulation film formed above the second electrode wiring layer; and
a second contact wiring layer buried in a second contact hole bored above the first contact wiring layer of the fourth insulation film and the second insulation film to connect the second electrode wiring layer and the first contact wiring layer.
Further, the semiconductor device according to the present invention comprises:
a switching transistor including a drain region and a source region which are comprised of an impurity-diffused region formed in the surface layer portion of a semiconductor substrate;
a first insulation film formed above the semiconductor substrate containing the transistor;
a wiring which is connected to one of the drain region and the source region through a contact wiring formed in a state buried in the first insulation film, the wiring being formed on the first insulation film;
a capacitor contact wiring formed in the first insulation film, the lower end of the capacitor contact wiring being connected to the other one of the drain region and the source region;
a second insulation film comprised of one of a nitride-based film and a titanium oxide film formed on the first insulation film containing the wiring;
a third insulation film formed above the semiconductor substrate containing the second insulation film;
a capacitor formed above the third insulation film and comprising a lower electrode, an inter-electrode insulation film composed of one of ferroelectric and high-permittivity dielectric, and an upper electrode; and
an electrode wiring which connects the upper electrode of the capacitor and the upper end of the capacitor contact wiring;
Further, the semiconductor device according to the present invention comprises:
a switching transistor including a drain region and a source region which are comprised of an impurity-diffused region formed in the surface layer portion of a semiconductor substrate;
a first insulation film formed above the semiconductor substrate containing the transistor;
a capacitor contact wiring formed in a state buried in the first insulation film, the lower end portion of the capacitor contact wiring being connected to one of the drain region and the source region;
a second insulation film comprised of one of a nitride-based film and a titanium oxide film formed on the first insulation film;
a capacitor formed above the second insulation film and comprising a lower electrode, an inter-electrode insulation film composed of one of a ferroelectric and high-permittivity dielectric, and an upper electrode;
an electrode wiring which connects the upper electrode of the capacitor and the upper end of the capacitor contact wiring to each other; and
a wiring formed above the semiconductor substrate and connected to the other one of the drain region and the source region.
Further, the semiconductor device according to the present invention comprises:
a switching transistor including a drain region and a source region which are comprised of an impunity-diffused region formed in the surface layer portion of a semiconductor substrate;
a first insulation film formed on the semiconductor substrate containing the transistor;
a capacitor formed on the upper layer side of the first insulation film and comprising a lower electrode, an inter-electrode insulation film composed of one of ferroelectric and high-permittivity dielectric, and an upper electrode;
one of a silicon nitride film and a titanium oxide film formed directly on the capacitor;
an electrode wiring which connects one of the drain region and the source region and one of the upper electrode and the lower electrode of the capacitor to each other; and
a wiring formed on the semiconductor substrate and connected to the other one of the drain region and the source region;
Due to the constitution described above, the semiconductor device and the method for the manufacture thereof according to the present invention, it becomes possible, in the manufacture of ferroelectric memory cells, to prevent the deterioration in characteristics of the ferroelectric capacitors and to realize process integration.
Further, means which can protect semiconductor device from being damaged by hydrogen or water is obtained.
Moreover, the deterioration in the amount of remanent polarization of ferroelectric films can be held down low.
Further, the deterioration of high-permittivity dielectric films or ferroelectric films due to reducing atmospheres can be prevented.
Further, the wiring layer and the element which have already been formed before the formation of a high-permittivity dielectric film or a ferroelectric film can be protected from oxidation, and thus, the conductivity and shapes thereof can be maintained and supplied in good condition.
In addition, in case of manufacturing ferroelectric memory having a multi-layer wiring structure consisting of at least two or more layers, the bit lines connected to the cells can be formed of multi-layer wirings, so that the composite or joint mounting thereof with other devices is facilitated.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.